Data on patents point to research and development trends and indicate where companies and investors are placing their bets. But whether the number of patents is a measurement of innovation remains a hot debate.

“In fuel cell, you are still in the intense research and development phase,” Cardona said. “People are spending a lot of time and money on the patents, but it’s not much of a commercial market yet.”

The firm, based in Albany, New York, has been tracking cleantech patents since 2002. It releases quarterly and annual reports called the Clean Energy Patent Growth Index, showing the number of patents by sectors, states and countries.

Fuel cell researchers and companies continue to file more patents than those in other sectors, including solar, wind, electric cars, biofuels and wave energy. Fuel cell patents, numbered 124, made up 56 percent of the total cleantech patents granted in the first quarter this year.

Patents for wind, tidal/wave and geothermal have gone up (see charts below). The patent office granted 35 patents for wind energy, four for geothermal and nine in tidal/ocean.

Those in solar, hybrid/electric vehicles and biomass/biofuel are heading down (see charts below). Twenty-three patents went to solar and 19 to hybrid/electric vehicle, for example.

Foreign companies are as active at securing patents as U.S. firms, Cardona said. In fact, the split is about 50-50 for the cleantech patents granted in 2007. U.S. companies had fewer in the solar sector but outpaced others in the biomass/biofuel segment.

For the first quarter this year, Honda Motor received 16 patents, the most of any company. General Electric followed with 11 patents, and General Motors got six.